Collaborative Research: Fundamental Properties of Local Subdwarfs

关于银河系的形成和演化，许多悬而未决的问题都需要提高对银河系晕和厚盘中局部金属贫乏亚矮星的运动学和化学富集模式的了解，以及如何将它们与球状星团恒星进行比较。即使经过最近的几次努力，目前的样本也不能充分覆盖在球状星团中看到的金属丰度和运动学范围，而对当地金属匮乏的巨星的观察提供了诱人的证据，证明当地晕星和具有相同金属丰度的球状星团中的恒星之间存在显著差异。这个项目将通过获得精确的、自一致的温度、变红和组成测量来改善观测情况，这些测量是对最近对金属贫乏恒星的调查中发现的大约150个经过严格挑选的亚矮星样本进行的。还将有新的理论努力来探索主序层亮度与详细的恒星化学成分和经常被忽视的物理（如氦扩散和旋转）之间的依赖关系。该项目还将提供关于晕和厚盘金属贫乏尾部的运动学和恒星形成历史的有价值的信息，识别在丰度模式和运动学上与球状星团恒星非常匹配的亚矮星样本，并提高球状星团主序的温度和丰度尺度，以便与巨大分支的光谱测定进行比较。还将对球状星团的相对和绝对年龄进行系统的研究，重点是减少理论层面上的误差。重要的是，该项目将使社区能够充分利用未来的FAME和sim卫星任务，这将测量样本中亚矮星的精确视差，从而产生球状星团主序亮度的绝对校准，从而获得它们的距离。目前的距离估计仅好于10 - 15%，导致年龄误差约为30%，不足以可靠地探索球状星团系统中的年龄分布，甚至不足以与恒星演化理论的预测相比较，为宇宙的年龄设定下限。

AST 0205789TerndrupMany outstanding issues concerning the formation and evolution of the Milky Way require improvedknowledge of the kinematics and chemical enrichment patterns of local metal-poor subdwarfs in theGalaxy's halo and thick disk, and how these compare to globular cluster stars. Even after several recentefforts, current samples do not adequately cover the range of metallicities and kinematics seen in globularclusters, while observations of local metal-poor giants give tantalizing evidence of significant differencesbetween local halo stars and those in globular clusters of the same metallicity.This project will improve the observational situation by obtaining accurate and self-consistentmeasures of temperature, reddening, and composition for a critically selected sample of approximately150 subdwarfs identified in recent surveys for metal-poor stars. There will also be new theoretical effortsto explore the dependence of the main-sequence luminosity on detailed stellar chemical composition andon often-neglected physics such as helium diffusion and rotation. This project will also yield valuableinformation on the kinematics and star formation history of the halo and the metal-poor tail of the thickdisk, identify samples of subdwarfs that are well matched in abundance patterns and kinematics toglobular cluster stars, and improve the temperature and abundance scales of globular cluster mainsequences for comparison to spectroscopic determinations on the giant branch. There will also be asystematic study of the relative and absolute ages of globular clusters, with a focus on reducing the errorsin the theoretical plane.Importantly, this project will enable the community to take full advantage of the future FAME andSIM satellite missions, which will measure accurate parallaxes for the subdwarfs in the sample andthereby yield the absolute calibration of the main-sequence luminosity for globular clusters and hencetheir distances. Current distance estimates are only good to 10 - 15%, resulting in age errors of about30%, insufficient to reliably explore the age spread in the globular cluster system or even set lower limitsto the age of the Universe by comparison with the predictions of stellar evolution theory.